Cellulosic materials which may be converted into valuable intermediates, which intermediates may be further processed into fuel components, are of considerable interest as feedstocks for the production of sustainable biofuels. Biofuels are combustible fuels, that can be derived from biological sources. The use of such biofuels results in a reduction of greenhouse gas emissions. Such biofuels can be used for blending with conventional petroleum derived fuels. Biofuels used for blending with conventional gasoline fuels include alcohols, in particular ethanol. Biofuels such as fatty acid methyl esters derived from rapeseed and palm oil can be blended with conventional diesel fuels. However, these biofuels are derived from edible feedstock and so compete with food production.
Biofuels derived from non-edible renewable feedstocks, such as cellulosic material, are becoming increasingly important, both economically and environmentally. In addition there has been much interest in developing improved methods for producing biofuels derived from non-edible renewable feedstocks, such as cellulosic material. Fuel components can be derived from cellulose derivatives using multistep processes, for instance levulinate (Bozels et al., Resources, Conservation and Recycling 2000, 28, 227), valerate (WO 2006/067171) or pentenoate (WO 2005/058793) esters from levulinic acid or methyl-furan (Roman-Leshkov et al., Nature 2007, 447, 982) or ethyl furfuryl ether (WO 2009/077606) from furfural.
It would, however, be advantageous to be able to convert cellulosic material such as for example lignocelluloses into a liquefied product, which liquefied product could then be fed to an oil refinery for upgrading to fuel components.
WO 2005/058856 describes a process for liquefaction of cellulosic material. In the process solid cellulosic material is heated in the presence of an acid catalyst and a solvent. The solvent contains a compound having a gamma lactone group of a specific general molecular formula. Examples of such compounds that are mentioned include gamma-valerolactone. It is further indicated that also levulinic acid, furfural or compounds without a gamma lactone group that are obtainable from levulinic acid or furfural may be used as solvent in the process. The process is suitable for its purpose, but unfortunately the large amounts of expensive solvent that are needed make the process economically less attractive.
U.S. Pat. No. 5,608,105 describes a process for producing levulinic acid from carbohydrate-containing materials. It describes as an example reacting a slurry of paper sludge containing 3.5% by weight of the aqueous portion sulfuric acid with steam in a series of two reactors. The liquid product outflow contains levulinic acid at a concentration of 0.68%. A disadvantage of the described process is that the process produces large amounts of low-value insoluble humins and, therefore, offers poor utilization of the feedstock. In addition the process is an extensive process using two reactors.
There remains a continuing need for the development of improved processes for liquefying cellulosic material.